Outcomes for patients who undergo weight-loss surgery may be influenced by vitamin D levels, according to a new study by researchers from Johns Hopkins Medicine.

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Exposure to sunlight is a key factor in vitamin D levels, but researchers found bariatric surgery patients from areas with less sunshine were more likely to experience postoperative complications.

Vitamin D plays a number of important roles in the body; it helps maintain bone health, aids immune system function and supports lung and heart health, among numerous other functions.

Exposure to sunlight is a key factor in vitamin D levels; ultraviolet radiation from the sun triggers vitamin D synthesis in the body. As such, people with low sun exposure often have lower vitamin D levels, which has been linked to numerous health problems.

Now, in a new study published in the journal Obesity Science & Practice, researchers suggest low vitamin D levels may worsen outcomes for patients undergoing weight-loss surgery, or bariatric surgery.

Study leader Leigh Peterson, of the Centers for Bariatric Surgery at Johns Hopkins, and colleagues found individuals in the US who underwent weight-loss surgery in winter – when vitamin D levels are at their lowest – were more likely to experience complications than those who had the surgery in summer.

In addition, the team found bariatric surgery patients from the northern US – where there is typically less sunshine – had poorer outcomes than bariatric surgery patients from sunnier southern areas.

“Sun exposure is critical in the synthesis of vitamin D, so the notion that people living in less sunny northern states may suffer from vitamin D deficiency is not surprising,” notes Peterson. “What is remarkable is how closely sun exposure, vitamin D and surgical outcomes were linked.”

To reach their findings, the team analyzed the outcomes of 932,091 patients of an average age of 43 who underwent bariatric surgery in the US between 2001-10.

Fast facts about bariatric surgery
  • The number of bariatric surgeries in the US increased by around 15% between 2011-13
  • Around 179,000 people in the US underwent bariatric surgery in 2013
  • The most common bariatric procedures in 2013 were sleeve gastrectomy, roux-en-Y gastric bypass and gastric bands.

Learn more about gastric bands

They compared outcomes of those who had the surgery in winter (January-March), summer (July-September) or fall/spring (October-December and April-June).

Adverse outcomes from bariatric surgery were rare, with less than 1% of patients developing infections. Prolonged hospital stays – defined as spending more than 3 days in the hospital – were a more common outcome, according to the researchers, affecting almost 40% of patients.

The researchers found that patients who lived in areas north of South Carolina were much more likely to have experienced infection or a prolonged hospital stay after weight-loss surgery.

Around 150,000 more patients from northern states had an extended hospital stay than those in southern states. Accounting for the 300,000 surgeries in the study that led to prolonged hospital stays, the team notes that 71% of all postoperative complications occurred in northern states.

Additionally, the researchers found that most adverse postoperative complications – such as wound infections, non-healing wounds and delayed wound healing – occurred in colder seasons with less sunshine. For example, around .16% of delayed wound healing cases occurred in winter, compared with 0.07% in summer.

According to the researchers, these findings suggest vitamin D may affect the outcomes of patients who undergo bariatric surgery, though they caution further research is warranted before the use of vitamin D supplements can be recommended to reduce postoperative complications for these patients.

Still, Peterson says the research may have important clinical implications:

The growing rates of obesity and increased popularity of bariatric surgeries mean that primary care clinicians and bariatric surgeons should consider screening their patients and correcting any confirmed vitamin D deficiency.”

One limitation of the study is that the researchers did not have a direct measure of patients’ vitamin D status through serum 25(OH)D concentration, with levels only being defined by vitamin D season, which could have affected the results.

On the back of this, the researchers say it is possible that other seasonal differences could have contributed to patient outcomes, noting that exposure to specific infectious agents is greater in winter. “Future studies should be conducted measuring 25(OH)D to confirm our findings,” they add.

Medical News Today recently reported on a study that linked low vitamin D levels to irritable bowel syndrome (IBS).